Disease manifestation and severity from acute infections are often due to hyper‐aggressive host immune responses which change within minutes. Current methods for early diagnosis of infections focus on detecting low abundance pathogens, which are time‐consuming, of low sensitivity, and do not reflect the severity of the pathophysiology appropriately. The approach here focuses on profiling the rapidly changing host inflammatory response, which in its over‐exuberant state, leads to sepsis and death. A 15‐min label‐free immune profiling assay from 20 µL of unprocessed blood using unconventional L and Inverse‐L shaped pillars of deterministic lateral displacement microfluidic technology is developed. The hydrodynamic interactions of deformable immune cells enable simultaneous sorting and immune response profiling in whole blood. Preliminary clinical study of 85 donors in emergency department with a spectrum of immune response states from healthy to severe inflammatory response shows correlation with biophysical markers of immune cell size, deformability, distribution, and cell counts. The speed of patient stratification demonstrated here has promising impact in deployable point‐of‐care systems for acute infections triage, risk management, and resource allocation at emergency departments, where clinical manifestation of infection severity may not be clinically evident as compared to inpatients in the wards or intensive care units.